As is known, seat belts in vehicles slide through D-rings that are connected to a fixed structure of the vehicle at a height above that of the shoulders of a user who must wear the seat belt.
To limit injury to the user in the event of an accident, it is advisable to provide expedients that enable the D-ring to cushion possible impact by the user's head.
To this end, U.S. Pat. No. 5,791,687 teaches how to connect the D-ring to a pillar by means of two brackets that plastically deform when the D-ring is pushed towards the pillar by a relatively high impact force. In particular, the D-ring is connected in a vertically sliding manner to an adjustment track, which is connected in turn to the brackets by respective bolts, spaced vertically apart from each other. The rear ends of the bolts pass through a front surface of the pillar and are fixed to the brackets, which are consequently housed inside the pillar.
A solution such as that described in U.S. Pat. No. 5,791,687 is not very satisfactory because the anchorage zone between the brackets and the rear ends of the bolts is relatively far from the D-ring, and so the load exerted by the seat belt during normal use could permanently deform some components. In fact, the tension exerted by the seat belt is directed substantially downwards and is transferred on the pillar through the two brackets, but the lever arm of the force with respect to the rear ends of bolts is relatively long, without any device that opposes flexure.
In addition, each bracket has an intermediate zone placed in contact against the front face of the pillar and is relatively far from the anchorage points to the front surface: therefore, in normal operating conditions, the above-stated flexure causes elastic deformation of the brackets, which vibrate against the front surface and consequently cause noise in the driver/passenger compartment.
Furthermore, it is relatively difficult to mount the system described in U.S. Pat. No. 5,791,687 in the vehicle, especially with regard to fastening the rear ends of the bolts to the brackets inside the pillar.